listed species are those with: 1) 5 or fewer extant sites, or 2) fewer than 1,000 individuals, or 3) restricted to fewer than 4 U.S.G.S. 7 ½ minute topographical maps, or 4) species listed as endangered by U.S. Department of Interior.

Federal Protection:
Not Listed

State Rarity Rank:S1

A State Rarity Rank of S1 means: This plant is endangered/critically imperiled in New York because of extreme rarity (typically 5 or fewer populations or very few remaining individuals) or is extremely vulnerable to extirpation from New York due to biological factors.

Global Rarity Rank:G5T1

A Global Rarity Rank of G5T1 means: Critically Imperiled globally - The subspecies/variety is at very high risk of extinction due to extreme rarity or other factors; typically 5 or fewer populations or locations in the world, very few individuals, very restricted range, very few remaining acres (or miles of stream), and/or very steep declines. (The species as a whole is common globally.)

Did you know?
Hudson River water-nymph is an endemic taxon in New York. In other words the only place in the whole world where it occurs is New York along the Hudson River. It is one of about three endemic taxa that occur in New York (Weldy and Werier 2005). The subspecific name muenscheri is named after Walter Muenscher (Clausen 1939) a botanist from New York who among other projects studied the aquatic plants along the Hudson River. According to Robert Clausen (1939), who named this taxon, Muenscher has contributed more than any other botanist to the knowledge of aquatic vegetation in New York.

This taxon is a globally rare New York State endemic. It is only known from the southern part of the Hudson River. Historically this species was quite abundant in the Hudson River from Piermont just south of the Tappan Zee Bridge north to the junction with the Mohawk River near Waterford. Over this range there are at least 20 distinct populations which have not been seen in over 70 years. There are 2 populations that are still known to be extant.

Short term trends for this taxon are unclear due to a lack of data. Some of the habitat where this species occurs has clearly been degraded by the invasive species Trapa natans. This might indicate that this species is declining in recent years but more evidence is needed.

There are at least 20 populations that have not been seen in recent years and only two populations which are currently known to be extant. It is likely that at least some of the historical populations are still extant but simply have not been seen recently because they have not been searched for recently. Also, it is likely that at least some of the historical populations have become extirpated since this was once considered an abundant species from Troy to Piermont (Muenscher 1937) and almost all of the previously known populations (20 out of 22) have not been documented in over 70 years. Long term trends are not clear due to lack of data but this taxon has most likely declined at least to some degree in the past 100 years.